Reptiles of North Carolina
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NC Records

Crotalus adamanteus - Eastern Diamond-backed Rattlesnake


Photo: Ed Corey
Taxonomy
Class: Reptilia Order: Serpentes Family: Viperidae Subfamily: Crotalinae Other Common Name(s): Eastern Diamondback Rattlesnake
Taxonomic Comments: Crotalus is a diverse genus of more than 50 species of venomous rattlesnake found across North and South America, from southern Canada to Argentina.

Species Comments: Crotalus adamanteus, the Eastern Diamond-backed Rattlesnake, is one of two Crotalus (and one of three rattlesnakes) in North Carolina. It is restricted to the southeastern United States from southeastern North Carolina to Florida, and west along the Gulf to the Mississippi River. In North Carolina, it was historically limited to the southeastern Coastal Plain, but populations have declined heavily due to habitat loss; it is now extirpated from the majority of its historical range in the state.

No subspecies are recognized.

The generic epithet Crotalus is derived from the Greek krotalon, "rattle". The specific epithet adamanteus is derived from the Latin adamanteus, "diamond-shaped".

Taxonomic References: McCranie (1980); Campbell and Lamar (2004); Means (2017)
Identification
Description: Eastern Diamond-backed Rattlesnakes are the largest and heaviest venomous snake in the area. Their head is large and much wider than the neck, and their tail features a long rattle. They are olive to brown with dark brown or black rhomboid/diamond blotches running the length of the body. These diamonds have pale margins and lighter centers. The distal portion of the tail is often black. There is a distinct dark postorital band bordered with whitish-yellow, and whitish-yellow vertical lines in front of the nostril. The venter is pale yellow to gray with dark mottling.

Juveniles and neonates have an enlarged "button" tail tip, rather than a rattle, and distinct tail bands, rather than a fully black tail.
Morphological Features: Eastern Diamond-backed Rattlesnakes typically have 27-29 heavily keeled dorsal scale rows at midbody. Ventral counts range from 159-187 (159-174 in NC specimens; Palmer and Braswell, 1995), with 20-33 (22-32) subcaudals and an undivided anal plate. Head scales are small, and counts are typically: 14 supralabials, 16-20 infralabials, 2 loreals, 2 preoculars, 4-5 post- and suboculars, and 2 nasals. Supraoculars are large and pronounced. Palmer and Braswell (1995) noted some variation in scalation across a small sample of specimens.

Eastern Diamond-backed Rattlesnakes have a maximum recorded total length of 251.5 cm (99 inches), though most are smaller. Palmer and Braswell (1995) reported a 184.8 cm captive male specimen from NC; the largest wild specimen they reported was a 183.5 cm male. Tail lengths account for only around 6-10% of total length. Males tend to have longer tails, more subcaudals, and fewer ventrals than females.

Eastern Diamond-backed Rattlesnakes are solenoglyphous, meaning they have large, elongated, hollow fangs that direct venom like a hypodermic needle. These fangs are extended out during a strike, and folded into the mouth when it is closed. Eastern Diamond-backed Rattlesnakes are dangerously venomous, and should not be handled. Their venom is hemotoxic, meaning it works by attacking the blood and causing hemorrhaging; local swelling, pain, tissue necrosis, and hemorrhaging at the bite site are common symptoms, as are secondary infections. Additionally, these rattlesnakes undergo an ontogenetic shift in venom composition (Rokyta et al., 2017).

Eastern Diamond-backed Rattlesnakes will coil and rattle vigorously when threatened, and may strike quickly and often without warning. Eastern Diamond-backed Rattlesnake bites have resulted in human fatalities. However, their first defense is to attempt to remain motionless and hidden, in order to avoid adverse interactions. Means (2017) recounts several instances of radio-tracking large Eastern Diamond-backs that resulted in stepping right next to (or even on top of) the snake he was tracking, without strikes or rattling.
Technical Reference: Palmer and Braswell (1995); Ernst and Ernst (2003, 2011); Campbell and Lamar (2004); Means (2017)
Field Guide Descriptions: Beane et al. (2010).
Online Photos:    Google   iNaturalist   GBIF
Observation Methods: Eastern Diamond-backed Rattlesnakes are extremely rare in the state, but is diurnal and occasionally found in stump holes and similar burrows.
Distribution in North Carolina
Distribution Comments: Quay (1959)'s inclusion of the Eastern Diamond-back Rattlesnake as a member of the Dare County barrier island herpetofauna was considered erroneous by Gaul and Mitchell (2007). There is no historical evidence this species ever reached North Carolina's barrier islands or made it north of Craven and Jones counties (Palmer and Braswell, 1995; Martin and Means, 2000).
County Map: Clicking on a county returns the records for the species in that county.
Key Habitat Requirements
Habitat: Diamond-backs appear to be primarily associated with mesic to wet flatwoods and peatland habitats in the Coastal Plain. These include lowland Longleaf Pine flatwoods and savannas, Carolina Bays, pocosins, and small-stream swamp forests (Palmer and Braswell, 1995; Beane et al., 2010).
Biotic Relationships: Small mammals are the principal prey of Eastern Diamond-backed Rattlesnakes. In his comprehensive treatise on this species, Means (2017) noted the importance of cotton rats (Sigmodon hispidus), cottontail rabbits (Sylvilagus sp.), and white-footed mice (Peromyscus sp.) to the diet of Eastern Diamond-backs. Other verified prey noted by Means (2017) include primarily small mammals: squirrels, flying squirrels, voles, various types of mice and rats, and domestic cats. Birds (including thrashers, sparrows, rails, turkey chicks, and bobwhites) have also been recorded. Most food records come from southern Georgia and Florida, though Palmer and Braswell (1995) noted rabbits found as prey of specimens from North Carolina.

Ophiophagous snakes—including coachwhips, kingsnakes, eastern indigo snakes, and possibly cottonmouths—are the most commonly reported natural predator of juvenile and adult Eastern Diamond-backed Rattlesnakes. As noted by Means (2017), there are very few documented records of natural predation on Eastern Diamond-backs otherwise, and most predator lists occurred in captive settings or are based on assumptions and/or extrapolation of records of other rattlesnake species. Means (2017) suggested that hawks may be important predators of these snakes and noted two documented interactions of Red-tailed Hawks predating young Eastern Diamond-backs. Bobcats and feral hogs have also been reported killing and consuming Eastern Diamond-backed rattlesnakes.
Life History and Autecology
Breeding and Courtship: Sexual maturity may not be reached until body lengths greater than 100 cm. Little is known about the reproductive habits of Eastern Diamond-backed Rattlesnakes in North Carolina. Elsewhere, two mating periods—one in spring and one in fall—are thought to occur.
Reproductive Mode: Eastern Diamond-back Rattlesnakes are ovoviviparous, giving birth to young enclosed in an amniotic sac; young are typically born July to October. Litters average 13 neonates.

Neonates average 37 cm in total length and weigh 40 g on average. Contrary to popular belief, neonate and juvenile rattlesnakes are not more venomous (or more likely to envenomate) than adults; juvenile venom glands are substantially smaller, and thus venom capacity is much smaller.
Terrestrial Life History: Little is known of the life history of Eastern Diamond-backed Rattlesnakes in North Carolina and given the near extirpation of the species from the state, nearly all information comes from populations elsewhere in the southeastern US. Generally, these rattlesnakes are secretive, spending much of their time under logs or other cover, or in stump holes and mammal burrows. The majority of all records of this species are of diurnal, terrestrial activity, though infrequently they will be active at night and climb to pursue prey. Though terrestrial, they are also good swimmers, frequently crossing both small bodies of fresh- and saltwater. Records from North Carolina include every month but December and January, with most coming from summer (June and August) and early fall (September–October).

Home range estimates are not known from North Carolina. Populations in Florida were reported to have large average home ranges: 46–80 hectares (460,000–800,000 m2) for females and 80–200 ha (800,000–2,000,000 m2) for males (Means, 1985; Timmerman, 1995).
General Ecology
Adverse Environmental Impacts
Status in North Carolina
NHP State Rank: S1
Global Rank: G3
Status in North Carolina: E

Photo Gallery for Crotalus adamanteus - Eastern Diamond-backed Rattlesnake

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Recorded by: Ed Corey
Onslow Co.
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